By Benjamin Bederson

The APS Historic Sites Committee (HSC) named four sites to honor in 2011. These were: the old Bell Telephone Laboratories in New York City (Davisson-Germer experiment), the Scripps Oceanographic Institute, La Jolla, California (Keeling Curve), the Brookhaven National Laboratory, Upton, NY, for general outstanding accomplishments, and the National Bureau of Standards (now NIST), Washington DC (non-conservation of parity). The 2011 HSC committee consists of Ruth Howes, J. David Jackson, Kurt Gottfried, and Benjamin Bederson (Chair).

Bell Telephone Laboratories

The Westbeth artists community in New York City was honored on May 9. It is named after its location on West and Bethuane Streets in Greenwich Village. From 1898 until 1966 it was the home of the famous Bell Telephone Laboratories, with the address 463 West St, before the laboratories moved to Murray Hill NJ. It was here that many of the twentieth century's most significant technological and scientific advances took place, for example crucial advances in electronics, radio, television, and radar. It was at this location that Claude Shannon made his landmark contributions to information theory, playing a crucial role in the development of computers. APS singled out a specific set of experiments, led by physicist C J. Davisson, for recognition. In 1927 at this site, he, along with L.H. Germer, showed that free electrons exhibited wave-like properties, under certain circumstances. This was the final link that established the reality of quantum mechanics. Davisson received the Nobel Prize for this work in 1937.

After the move to Murray Hill the West Street group of buildings was renovated by the architect Richard Meier and was taken over by what is now the Westbeth artists condominium. It has become a thriving center of artistic culture on the New York scene.

A plaque was installed at the site, reading:

At this site, the original location of Bell Telephone Laboratories, in 1927 C. J. Davisson and L. H. Germer performed the first direct demonstration of the wave-like behavior of elementary particles, predicted by L. de Broglie in 1923. The Davisson-Germer experiment provided crucial empirical evidence for the validity of the then rapidly evolving theory of quantum mechanics. In those years and subsequently many important scientific and technological discoveries were made at the same laboratory.

The President of the successor to Bell Labs, Alcatel-Lucent Bell Labs, H. Kim Jeung, and Alice White, Chief Scientist, attended the dedication as well as representatives of the Westbeth community. Presiding was Curtis Callen, Past APS President. To our knowledge this was the first formal meeting of the two groups—artists and scientists—a striking confluence of the two cultures.

Scripps Oceanographic Institute

On June 17 we honored the Scripps Institute of Oceanography for the lifetime achievement of Charles Keeling in demonstrating the annual increase in the concentration of carbon dioxide in the atmosphere. This accomplishment revealed hard evidence of the impact of human activity on the concentration of greenhouse gases in the atmosphere. The citation reads:

The Keeling Curve and the Scripps Institution of Oceanography. At this location Charles David Keeling planned and led his project to measure the level of carbon dioxide gas in the atmosphere. The rise of the level over the decades reveals an influence of human activity.

In 1957 Roger Revelle, Director of Scripps, and Hans Suess, a staff member, published a prediction that there would be a buildup of carbon dioxide gas in the atmosphere, since the oceans could not absorb the gas as rapidly as human industry was emitting it. For more than half a century scientists had speculated that a rise in the gas would have a strong effect on global climate, so Revelle decided to check whether the level of carbon dioxide was in fact rising. He hired Charles David ("Dave") Keeling (1928-2005), a young postdoc who had already been making measurements of the gas because of its important role in geochemistry and agriculture.

Keeling's measurements were done with physical instrumentation that he had developed himself, and which was much more precise than previous systems for measuring atmospheric carbon dioxide. He measured the gas's absorption of infrared radiation-the same physical phenomenon that produces the so-called "greenhouse effect". (Carbon dioxide, water vapor, and other "greenhouse gases" trap heat as it radiates from Earth into space; if there were no carbon dioxide in the atmosphere, our planet would be mostly frozen.) By going to pristine locations Keeling was able to determine a true baseline level.

The plan was to take a "snapshot" of the planet's carbon dioxide levels at a number of locations during the International Geophysical Year (IGY) 1957-1958, and then repeat the observations a few decades later to see whether the predicted rise had occurred. But Keeling was so dedicated to precision that he was able to detect a rise within two years. These first results, published in 1960, were done with instruments in the extremely pure air of Antarctica. Keeling was meanwhile gathering measurements from other parts of the globe, of which the most significant came from a station near the summit of Mauna Loa in Hawaii, located in mid-Pacific in the pure air above the tropical inversion layer.

The Mauna Loa curve rose steadily year by year, in a sawtooth pattern as plants in the Northern Hemisphere took up carbon dioxide during their spring growth and released it in autumn and winter decay-a phenomenon that Keeling exploited for significant studies of the carbon cycle. By the early 1970s the rise of the curve was accepted by scientists as highly significant.

Meanwhile theoretical studies suggested a strong likelihood that the additional gas would eventually produce a profound global warming. From the 1980s to the present, as the world's scientific academies, governmental agencies, and intergovernmental panels increasingly voiced worries about future climate change, the ever-climbing "Keeling Curve" became an icon familiar to all concerned members of the public. These measurements are fundamental to all studies of climate change.

After his death the work at Scripps has continued under the direction of his son, Ralph Keeling.

Brookhaven National Laboratory

On September 23 we honored the Brookhaven National Laboratory for its many discoveries—you might say, for a lifetime's achievement. The citation reads:

At this laboratory, over many years, physicists and engineers have made numerous fundamental discoveries in the fields of nuclear and high energy physics, the physics and chemistry of materials, energy and environment, biology and medicine. Among many landmark experiments are establishing the spin direction (helicity) of the electron neutrino, first observation of solar neutrinos, proof of more than one species of neutrinos, first observation of a lack of symmetry between matter and antimatter, and the principle of strong focusing that led to more compact and powerful accelerators.

A convocation to celebrate the award was held September 23 in the Berkner Hall Auditorium. The lead article in the BNL publication The Bulletin of October 14 describes the event in detail; part of it, including a summary of the four talks presented, appears below.

Historic Site Hurrah at BNL

Heavy rain fell on Friday, September 23—the day that the American Physical Society (APS) recognized Brookhaven National Laboratory as a historic site in the advancement of physics. The planned walking tour was postponed, but members of the Lab community, undaunted by the weather, gathered in Berkner Hall to attend the award ceremony.

The purpose of the APS Historic Sites initiative is to increase public awareness of physics and physicists' awareness of important past scientific advances and their place in the historic evolution of their work. Brookhaven is now one of about 20 historic sites designated by the APS, this being the first time an entire national laboratory has received this prestigious recognition.

"This is a tremendous event at the Laboratory for all of us who work here now, those who worked here in the past, and those who will work here in the future," said Laboratory Director Sam Aronson, as he welcomed everyone to the ceremony.

Robert Crease, BNL historian and Stony Brook University Philosophy Department chair, gave the first talk. "The history of Brookhaven is one of the most important stories of post-World War II science," said Crease, highlighting some of the important people, facilities, and scientific developments in the evolution of BNL during its six- decade-plus history.

BNL Senior Physicist Emeritus, former APS Editor-in-Chief, and former BNL Deputy Director Martin Blume spoke next. Blume focused on the story of two Brookhaven scientists: Renate Chasman and Kenneth Green. They developed the Chasman-Green Lattice—an arrangement of magnets that bends, focuses, and corrects an electron beam. This lattice is a critical component for BNL's National Synchrotron Light Source (NSLS), other light sources around the world, and the future NSLS-II.

"The development of a design expressly for a synchrotron radiation source, with a labora- tory staff that could make varied use of it and colleagues in many universities and industrial laboratories, showed the advantage of a multidisciplinary laboratory like Brookhaven," Blume said.

Nicholas Samios, director of the RIKEN BNL Research Center and former Brookhaven Laboratory director, then discussed physics discoveries and contributions resulting from work done through the Laboratory's facilities and major programs. "Major programs are important because although you can't pick one big thing, they greatly add to a body of knowledge," Samios noted.

National Bureau of Standards (now NIST)

The final convocation took place on November 9, at the former site of the National Bureau of Standards, now NIST, which is now partially occupied by the University of the District of Columbia, where the plaque will be installed. The installation is in honor of the landmark non-conservation of parity experiment performed there by a group of NBS scientists headed by Ernie Ambler, in collaboration with the Columbia University physicist C. S. Wu. The citation reads:

Non-conservation of Parity in Weak Interactions. At this location in 1956, C.S. Wu, E. Ambler, R.W. Hayward, D. D. Hoppes, and R.P. Hudson measured the asymmetry of the angular distribution of electrons emitted by polarized 60Co nuclei demonstrating that weak interactions are not symmetric under a change of parity. This work led to the recognition that the weak and electromagnetic forces are aspects of a single force.

It was long believed that in both classical and quantum physics the laws of nature do not distinguish between pairs of physical processes that differ only by mirror symmetry, which interchanges left and right. Before 1955 it was generally believed consistent with experiment that all physical interactions are symmetric when left and right are interchanged.

After World War II, physicists rapidly discovered a zoo of new particles. One of the new particles, the K+ meson, decayed sometimes to two pions (positive parity) and sometimes three pions (negative parity). Clearly, there were either two nearly identical particles that decayed in different ways or the parity symmetry did not hold for a single particle (now known as the K+ meson. In 1956 T.D. Lee (Columbia University) and C.N. Yang (Brookhaven National Laboratory), studied this puzzle. Their careful review of the literature revealed that while there was lots of evidence that interactions governed by the strong nuclear force (nuclear physics) and the electromagnetic force (atomic physics) were symmetric under a change of parity, the symmetry had never been tested experimentally in interactions governed by the weak force such as beta decay in nuclei and the decays of particles like the K+. In a 1956 paper, Lee and Yang proposed experiments to test the conservation of parity in systems governed by weak interactions. For this work, they were awarded the 1957 Nobel Prize in Physics.

One of the experiments that Lee and Yang proposed was to measure the changes in the distribution of electrons emitted in the beta decay of 60Co along the axis of nuclear polarization as the direction of polarization was changed from up towards the detector to down away from the detector. 60Co was an ideal candidate for this test. Its beta decay was well-studied and governed by a single matrix element so there would be no interference terms to provide background in the measurement. Cobalt is ferromagnetic and so the nuclei could be polarized by placing them in a strong magnetic field at very low temperatures. The experiment sounds simple; however, it posed major challenges. The source had to be kept at temperatures below 0.01K and placed in a magnetic field of 2.3 tesla. The radioactive nuclei had to be very close (50 μm) to the surface of the material so that the electrons would not interact with the molecules of the crystal after beta decay. Finally the electron detector had to be placed inside the dewar if decay electrons were to be detected. Remember that at this time electronics were vacuum tube and low temperature seals were made with soap. Growing crystals with thin radioactive surface layers was anything but an established field.

C.S. Wu, a leading expert on beta decay and Lee's colleague in the Physics Department at Columbia University, and Ernest Ambler, an expert on low temperature spin polarization and his colleagues at the low temperature laboratory of the National Bureau of Standards, accepted the challenge of conducting the experiments. In January 1957, they submitted a paper to Physical Review presenting the results of their experiments conducted in late 1956. The experiment demonstrated conclusively that interactions governed by the weak force are not symmetric under a change of parity.

The results of the beta decay experiment by C.S. Wu, E. Ambler, R.W. Haywood, D.D. Hoppes, and R.P. Hudson were confirmed by experiments on the decay of μ-mesons published by Garwin, Lederman and Weinrich in the same issue of Physical Review. The demonstration that weak interactions are not symmetric when a system's parity is changed lead to new theoretical understanding of neutrinos, the role of fundamental symmetries in shaping the physics of the universe, and the eventual unification of the weak and electromagnetic forces.

A small ceremony was conducted at the University Board Room, attended by the university president Allen Sessoms, Katharine Gebbie, Director, Physical Measurement Laboratory, NIST, APS Executive Officer Kate Kirby, Allen Chodos, Benjamin Bederson, and a number of UDC teachers and administrators.

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The articles in this issue represent the views of their authors and are not necessarily those of the Forum or APS.